The following Patent Document 1 discloses a method in which a rotor driving motor is rotated in a constant velocity in advance, information of rotational velocity fluctuation of a driving shaft at that time is stored in a storage means, and the information of the rotational velocity fluctuation (change) is read from the storage means so as to change the velocity of the driving motor.
Patent Document 1: Japanese Patent No. 2,754,582
There is an image forming apparatus using an electrophotographic system, as follows. That is, an electrostatic latent image is formed on a photoconductor by laser scanning, and toner is applied to the electrostatic latent image by a developing means. A toner image formed thus is transferred to an intermediate transfer belt by a first transfer means. Next the toner image is transferred from the intermediate transfer belt to paper by a second transfer means.
The image forming apparatus generally uses a motor and a reducer for rotating and conveying a driving roller for a photoconductor drum or a photoconductor belt, a driving roller for the intermediate transfer belt, etc.
Gears are chiefly used as the reducer in view of cost. Due to eccentricities of the gears, single pitch errors and cumulative pitch errors of gear teeth, etc., rotational fluctuation appears in the output shaft of the reducer in spite of constant-velocity rotation of the motor. The rotational fluctuation leads to image unevenness on the photoconductor or the intermediate transfer belt. Thus, the image quality deteriorates.
In the background art, there has been proposed a method in which rotational fluctuation is detected by an encoder attached to a transfer drum shaft, and a motor is controlled to cancel the detected rotational fluctuation.
However, in order to detect the rotational fluctuation of a reducer accurately up to a high frequency, a high-precision encoder is required. Thus, the apparatus cost increases. When a low-price encoder is used, only a comparatively low frequency component corresponding to one turn of a photoconductor, a photoconductor driving roller or an intermediate transfer driving roller can be corrected.